The invention concerns a method for analysis of the pressure variation in a perfusion device including several perfusion modules each equipped with a pump to impel a liquid to be perfused in a line placed downstream from the pump as well as means for measuring the pressure in the line, with junction points enabling connection of certain lines with each other or certain lines with lines originating in units external to the perfusion device as well as a perfusion device for implementation of the process.
Perfusion devices usually include a source of liquid connected to a flexible tube which is extended by a cannula or a catheter designed to be inserted into the patient""s body. To ensure a controlled flow rate of the liquid, it is common to place a pump along the tube. This pump, when it is of the syringe type, also contains the source of liquid.
When multiple products are to be injected, it is sometimes necessary to use a plurality of these perfusion units. The lines from certain pumps may be connected to each other to allow mixing of different products. The different units are equipped with control means which can trigger alarms or even interrupt the perfusion when certain control criteria are verified.
Proper progress of the perfusion may, in certain cases, be vital. It is thus imperative that the product be administered in accordance with the intended administration plan.
However, incidents sometimes develop which disrupt the progress of the perfusion of one of the products. These incidents are of three types:
an obstruction in the line downstream from the pump;
a rupture of the line downstream or upstream from the pump, or an obstruction upstream from the pump;
a variation in the flow rate in a pump whose line is connected by a junction point with other lines (for example, in the case of a bolus).
These incidents all translate into a variation of pressure in the affected line. Thus, an increase in the pressure in the line k will be noted, for example, in the following cases:
obstruction in the line k;
increase in the flow rate, for example, within the framework of a bolus, in a line j connected to the line k by a junction point.
On the contrary, a reduction in pressure will be noted, for example, in the following cases:
rupture of the line;
reduction in the flow rate in a line j connected to the line k by a junction point.
In the prior art devices, each perfusion unit, or module, is generally equipped with means to monitor and analyze the pressure variations in order to trigger alarms and, as appropriate, to interrupt the perfusion. Thus, if the pressure measured in the line exceeds a certain value, an alarm is triggered and the pump of the affected module is stopped. The user, generally a member of the medical staff, must then determine the cause of the abnormal increase in pressure. If there is no explanation for the increase, for example, this pressure increase is not the result of a manual bolus, it must be concluded that an obstruction has occurred downstream from the pump. However, since the occurrence of the obstruction, the pump has continued to pump until the pressure in the line reaches an alarm value. If the obstruction is eliminated suddenly, all the liquid under excess pressure downstream from the pump and which should have been administered over a certain period of time is delivered abruptly. To prevent such a phenomenon, the pump affected by the obstruction is stopped, then operated in reverse to aspirate the quantity of liquid released since the formation of the obstruction, so as to completely eliminate the bolus. Only at this time can the obstruction be eliminated without danger.
This system of individual detection of pressure for each line from a pump is very effective as long as the affected line is not connected to another line. However, in multiple unit perfusion devices, it is not rare that certain lines are connected in a junction point. If an obstruction develops downstream from such a junction point, the pump whose alarm threshold is the lowest will issue an alarm signal first and will begin to pump in reverse until the disappearance of the excess pressure in its line. However, the other pumps whose lines are connected at the junction point have not yet detected any obstruction because their alarm thresholds have not yet been reached. They thus continue to pump normally, feeding the excess pressure. The pump which is in reverse operation will thus not only aspirate what it delivered after the occurrence of the obstruction, but it will also aspirate the liquid delivered by the other pumps to which it is connected by the junction point. The liquid thus contained in the pump operating in reverse becomes indeterminate and can no longer be used without risk to the patient.
The same increase in pressure which caused the stopping of the pump k may be the result not of an obstruction but rather of a temporary (case of a bolus) or lasting increase in the flow of a line j connected to the line having detected the abnormal increase in pressure. The module k and the perfusion will thus have been interrupted unnecessarily.
An object of the invention is thus to perfect a process which enables avoiding malfunctions due to the fact that certain lines may be connected to each other.
This object is accomplished by the method in accordance with the invention wherein, when a pressure variation Pk in a line k is detected, an analytical process is implemented to determine the involvement of other modules j in this pressure variation. This process enables consideration of the environment of the affected module before acting, taking into account data from either another module or external data. For this, the modules must be able to communicate either among each other or with a base unit combining all the data and retransmitting them to the modules which may be affected by the data. The analytical process is launched both in the event of increase and in the event of decrease of pressure. Its objective is to analyze the environmental situation of the module affected, in order, depending on the results provided by this analysis, either to avoid an unnecessary interruption of the perfusion if the cause of this variation is explained (variation of the flow rate in a module connected by a junction point, manual bolus at a junction point with the affected line) or to simultaneously stop all the pumps affected by an obstruction or a rupture.
In a first variant, the process includes a search for data indicating a change in the flow rate in another module j. When the flow rate in one line is modified, the affected module sends out, automatically or on demand, a message concerning the modifications made. If a module k detects a pressure variation in its line, it searches for such a message. If it finds one, it will conclude that the pressure variation has a known explanation.
In a further development of this first variant, the analytical process provides, when a message indicating a modification of the flow rate in another module j has been found, for modification of the analytical parameters of the module k for at least the time the modification of flow in the module j lasts. Thus, if the module k notes that the flow rate has been increased in a second module, it modifies its analytical parameters such that it is no longer in an alarm situation. This modification may be of short duration, for example, the duration of a bolus, or lasting, if the increase in flow rate is prolonged. This process is of interest to prevent stopping the perfusion unnecessarily.
According to a second variant, the analytical process includes comparison of the slope of the pressure curve of each line i of the system with the slope of the pressure curve of the line k to determine the lines j which are potentially connected to the line k by a junction point and which may also be affected by the pressure variation. If, in a line j, a pressure increase similar to the pressure increase in the line k is noted, it is probable that the line j is connected to the line k by a junction point. Because of load losses and different means of measurement of pressure which may be used, it is possible that the pressure variations of the lines j and the line k may not be completely identical. It is possible, for example, to establish two thresholds of tolerance which will indicate, when they are reached, that the lines are definitely connected or that they are only probably connected to each other. This information enables better assessment of the interactions of these modules among each other to more precisely analyze the pressure variations in a line k.
A third variant provides for including in the analytical process the comparison of the rate of increase of pressure in the line k with the theoretical rate it should have if an obstruction developed in the line upstream from any junction point with another line. If the module is used alone, i.e., without connection to other lines, it is possible, based on the flow rate and the compliance of its constituting elements, to determine the theoretical rate of the pressure increase in the event of an obstruction in the line. If the line k in which a pressure increase has been detected is connected to other lines, the rate of the pressure increase in the module k will not correspond to the theoretical rate calculated for the same module considered in isolation. In contrast, if this rate is similar to the theoretical rate, it is very likely that the obstruction is located upstream from any junction point.
These three variant embodiments of the analytical process permit, on the one hand, to search for an admissible explanation for a pressure variation and, on the other, to determine whether the module in which the pressure variation has been detected is connected to other modules, and if so, what these modules are. However, these embodiments provide only initial information, which is sometimes inadequate. It is thus preferable to combine these variants in order to refine the analysis.
Thus, in a subvariant combining the second and the third variants, the analytical process includes the calculation of the theoretical rate of the pressure increase which should be observed in the line k in the event of obstruction downstream from junction points with the lines j and the comparison of the actual rate of increase in the line k with this theoretical rate. If the process according to the third variant reveals that the module cannot be considered to be isolated (consequently, that there is no obstruction upstream of any junction point with other modules), the process according to the second variant is implemented to determine what modules are affected by this pressure variation, i.e., those which are connected to the line k by a junction point. When it is known which other modules are affected, the theoretical rate of pressure increase in the line k if an obstruction was located downstream from the junction point of these modules is calculated using their respective flow rates and compliance parameters. If the actual rate corresponds to this new theoretical rate, it can be concluded that an obstruction has developed downstream from the junction point. Otherwise, it must be concluded that the pressure variation is probably due to a flow rate variation in a module connected to the module k or to a manual bolus at a junction point located on the line k. This hypothesis can be verified, for example, by performing the process according to the first variant.
From a practical standpoint, it is preferable to measure the pressure P1 in each line i at regular intervals and to store these measurements in a history file no later than the time when a pressure variation is detected in a line k. For certain applications, it is preferable to begin storage of the values as of the start of the perfusion in order to be able to determine, if an obstruction has developed, the instant when it occurred. It is not absolutely necessary to save the records during the entire period of the perfusion. For reasons of economy of memory, it may be preferable to store the data for only a certain period of time. This period of time will be determined based on the flow rate of the different pumps and thus on the time necessary to detect an obstruction.
Initiation of the analytical process when the pressure Pk in a line k reaches a threshold value established for each pump is within the scope of the invention. In practice, a lower threshold and upper threshold will be established for each module, with the normal pressure being between these two values. As soon as the pressure moves outside this tolerance range, the analytical process is initiated. It is possible to establish a second pair of threshold values included in the preceding range, which initiates an observation process, for example, recording the values measured.
When the results of the analytical process reveal that the pressure variation is due either to a rupture in the line (pressure reduction in one or a plurality of lines) or to an obstruction in a line (unexplained pressure increase in one or a plurality of lines), it is necessary to act as quickly as possible. That is why the method provides, when the results of the analytical process lead to the conclusion that a rupture or an obstruction has developed downstream from pump k, to stop the pump k and, as appropriate, the pumps j connected to the pump k by their respective lines at junction points located upstream from the rupture or the obstruction. Thus, not only the pump k which triggered the alarm is stopped, but so are the pumps j connected to the pump k by a junction point located upstream from the obstruction or the rupture. In the event of an obstruction, increasing the overpressure upstream from the obstruction by allowing each pump j to pump until its alarm threshold value is in turn reached is prevented. In addition, if the other modules k are not stopped, the liquids supplied by these modules will have a tendency to flow back into the line k under the effect of the pressure, resulting in an indeterminate mixture. This disadvantage is prevented by simultaneously stopping all the modules located upstream from the obstruction.
To avoid the bolus phenomenon when the obstruction is eliminated, it is in accordance with the invention to operate each pump j which was stopped for a period of time xcex94tj in reverse, at a reverse flow rate RQj proportional to the initial flow rate Qj at the time of normal operation. For this, the pumps which had the highest pumping flow rate Qs among the pumps j affected by the obstruction is determined, for example; this pump s is then run in reverse at a reverse flow rate RQs and the other pumps j at the respective reverse flow rate
xe2x80x83RQj=(Qj/Qs)xc3x97RQs
The period of time xcex94tj will be selected such that a bolus is avoided, on the one hand, and there is no aspiration of blood, on the other.
In a first variant embodiment of this process, the periods of time xcex94tj during which the pumps affected by the obstruction operate in reverse at the reverse flow rate RQj are selected identical for all said pumps and equal
xcex94t=(T2xe2x88x92T0)xc3x97xcexa3(Qj)/xcexa3(RQj),
where T0 is the time at which the obstruction occurred, this time T0 being determined by means of the history of measurements recorded from the beginning of the perfusion, and T2 is the time at which the obstruction was detected. To apply this variant, it is thus necessary to begin the recording of data concerning the pressure measurements from the beginning of the perfusion and it is necessary to save them long enough to be able to determine the time T0 at which the obstruction developed.
In a second variant embodiment of this process, each pump j affected by the obstruction operates in reverse until the pressure determined in its line has dropped below an established threshold Plj. For this variant embodiment, it is thus unnecessary to determine in advance a specific period of time xcex94tj, the monitoring of the pressure in each tube j being adequate to stop the affected pumps.
To facilitate the work of the medical staff, the result of the analytical process is displayed in the form of a diagram combining the various lines, for example, on a screen integrated with the base unit.
The object of the invention is also accomplished in that the multiple pump perfusion device is equipped with a device to implement the method according to the invention. This device to implement the method can be placed either directly on each pump if the pumps are capable of communicating with each other, or in an external control device connected to each pump, such as a computer or a base unit.